Equine Antibiotic Resistance Increased after Hospitalization

A team of researchers working at Philip Leverhulme Equine Hospital in Liverpool found that Escherichia coli bacteria in a horse's intestine appear to acquire antibiotic resistance while a horse is hospitalized.

The researchers found a significant increase in multiple drug resistance in E. coli samples isolated from horses' feces after a period of hospitalization.

The research was led by Adele Williams, BVSc, MRCVS, who had received funding from equine charity The Horse Trust. Williams carried out the research while undergoing a Horse Trust-funded clinical training program in equine internal medicine at the University of Liverpool.

Williams and colleagues collected fecal samples from randomly selected horses at Philip Leverhulme Equine Hospital over an 18 month period between 2006 and 2008. Fecal samples were collected when the horse was admitted, and again after the horse had been hospitalized for seven days. The selected horses included horses treated and not treated with antibiotics before and during hospitalization.

E. coli bacteria cultured from the samples were tested for their sensitivity to eight antibiotics (neomycin, ampicillin, ceftiofur, gentamicin, chloramphenicol, ciprofloxacin, tetracycline, and trimethoprim) using the Kirby-Bauer disk diffusion method. The antibiotics chloramphenicol and tetracycline are not used at the hospital.

The researchers found a significant increase in resistance during the week's hospitalization for seven of the eight antibiotics; no significant difference was found for neomycin. Antibiotic resistance increased even in horses not treated with antibiotics and to antibiotics that are not used in the hospital.

This increase might be due to the transfer of antibiotic resistant genes as a result of selection pressure for antibiotic resistance in the hospital environment, or it may be because the number of resistant E. coli is greatly increased due to selective pressure so that they are much easier to detect, or that resistant isolates have been acquired from the environment. Further research is needed to understand the source of antibiotic resistance in the environment.

"Pathogenic bacteria are likely to be exposed to the same selection pressures or could receive the same resistant genes, so it is vital we improve hygiene in equine hospitals and reduce the overuse of antibiotics," said Williams. "People who work in equine hospitals need to pay strict attention to hygiene and should reserve antibiotics for essential cases only."

Williams presented her research at the European College of Equine Internal Medicine Congress in January 2009.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.